Cable hoisting drums are used extensively in oil exploration for raising and lowering the drill string having the drill bit at the end. Since such a drill string can be hundreds of feet long and therefore extremely heavy, durable and powerful brakes must be utilized to control the rotation of the hoisting drum as it lowers thousands of pounds of drill string.
In the past, band brakes have been used on these hoisting drums, and these types of brakes are rather effective in certain aspects, including giving the operator a "feel" of whether or not the brake is actually controlling rotation of the drum, this feel being delivered to the actuating lever used by the operator. In addition, these band brakes are advantageous since they are self-energizing, i.e., the braking reaction force generated between the band and the drum assists in applying the braking force. However, these band brakes have several disadvantages. First, they wear out reasonably quickly and secondly they are time-consuming to replace, thereby interfering with the drilling operation. Moreover, band brakes are known to slip, especially under adverse weather conditions.
While hydraulic disk brakes would overcome these disadvantages, they have had up until now their own disadvantages of not being self-energizing and also not providing an actuating lever feel, or signal, to the operator that the braking action is actually taking place on the drum.
Examples of these known band brake systems and several disk brake systems are disclosed in the following U.S. Pat. Nos.: 2,308,499 to Eksergian; 2,490,941 to Bell et al; 2,781,871 to Altekruse; 2,992,860 to Hirzel; 2,999,567 to Adams; 3,058,547 to Tiley et al; 3,155,196 to Foxx; 3,386,536 to Davidson; 3,537,759 to Du Bois; 3,759,489 to Jones; 4,043,607 to Signorelli et al; 4,046,235 to Shutt; 4,074,891 to Ritter; and 4,144,953 to Johnson et al.